The present invention relates to an underwater buoy with modular members for suspending tubular ducts for transporting hydrocarbons between a seabed and a surface installation.
In order to raise hydrocarbons from an underwater well to the surface, tubular ducts are installed substantially vertically between the well and an underwater area situated below the surface of the water, after which these vertical tubular ducts are extended by generally flexible tubular ducts which join a surface installation. The substantially vertical tubular ducts are generally rigid and are held vertical by underwater buoys. The size of these underwater buoys and consequently the volume of air that they are able to trap can be adjusted as a function of the upward force that they must exert on the tubular duct in order to hold it vertical. This upward force also depends on the dimensions of the duct and its length, in other words the depth of water. Moreover, if the upward force to be exerted is relatively high, the volume of the underwater buoy must also be high. Furthermore, because it is difficult to transport buoys of large volume, transporting them in pieces has been envisaged, for example on laying ships, and then assembling them directly on site.
Thus the buoys comprise a frame and modular members that form floats adapted to be mounted on said frame when the buoy is installed. The modular members extend longitudinally between two opposite modular member ends. Said frame has a longitudinal hollow body adapted to receive said extended tubular duct and radial retaining means mounted on said hollow body hold said modular members substantially parallel to said hollow body and around said hollow body.
Reference may be made in particular to the document WO 03/064807, which describes one such underwater buoy.
However, when the modular members are relatively bulky so that the underwater buoy exerts a relatively high upward force, the retaining means are intensely loaded and there is a risk of them breaking.